Method of performing transmission and prioritization for radio link control packets for a medium access control layer of a wireless communications system

ABSTRACT

A method used in a medium access control, hereinafter called MAC, layer of a wireless communications system for performing transmission and prioritization for packets of a radio link control, hereinafter called RLC, layer including a plurality of RLC entities coupled to a plurality of logic channel includes determining a size of a MAC protocol data unit, hereinafter called PDU according to a grant provided by a lower layer, selecting MAC control elements for use in a MAC PDU header, determining MAC sub-headers for use in the MAC PDU header according to the selected MAC control elements, determining a total transmission payload size according to total sizes of the control elements and the MAC sub-headers, and then allocating a transmission payload size for each RLC entity according to the total transmission payload size, a data volume provided by each of the plurality of RLC entities, and logic channel priority.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for packet transmission andprioritization, and more particularly, to a method of performingtransmission and prioritization for packets of a radio link control(RLC) layer for a medium access control (MAC) layer of a wirelesscommunications system.

2. Description of the Prior Art

A long-term evolution (LTE) system, initiated by the third generationpartnership project (3GPP), is now being regarded as a new radiointerface and radio network architecture that provides a high data rate,low latency, packet optimization, and improved system capacity andcoverage. In the LTE system, an evolved universal terrestrial radioaccess network (E-UTRAN) includes a plurality of evolved Node-Bs (eNBs)and communicates with a plurality of mobile stations, also referred asuser equipments (UEs).

A radio link control (RLC) layer is responsible for data transfer ofradio bearers from an upper layer, Packet Data Convergence Protocol(PDCP) layer, and includes three transfer modes of Transparent Mode(TM), Unacknowledged Mode (UM) and Acknowledged Mode (AM). An RLC entityexchanges RLC service data units (SDUs) with upper layer and RLCprotocol data units (PDUs) with its peer RLC entity via lower layers. AnRLC PDU can either be an RLC data PDU or an RLC control PDU.

In the LTE system, a UM RLC entity is configured either as atransmitting UM RLC entity or a receiving UM RLC entity. Thetransmitting UM RLC entity receives RLC SDUs from upper layer and sendsRLC PDUs to its peer receiving UM RLC entity via lower layers. Thereceiving UM RLC entity delivers RLC SDUs to upper layer and receivesRLC PDUs from its peer transmitting UM RLC entity via lower layers. Inaddition, the transmitting UM RLC entity segments and/or concatenatesRLC SDUs in accordance to a transport block (TB) size selected by lowerlayer at the particular transmission opportunity when forming UM data(UMD) PDUs from the RLC SDUs.

In the LTE system, an AM RLC entity, either in the E-UTRAN or in the UE,consists of a transmitting side and a receiving side and supportssegmentation, retransmission, sequence check and other functions. Thereceiving side of the AM RLC entity delivers RLC SDUs to the upperlayers and receives RLC PDUs from its peer AM RLC entity via the lowerlayer. The transmitting side of the AM RLC entity receives RLC SDUs fromupper layers and delivers RLC PDUs to its peer AM RLC entity accordingto a TB size indicated by a medium access control (MAC) layer. Inaddition, the transmitting side of the AM RLC entity segments and/orconcatenates RLC SDUs in accordance to the TB size selected by the MAClayer at the particular transmission opportunity when forming AM data(AMD) PDUs from the RLC SDUs.

In AM data transfer, the transmitting side of the AM RLC entity shallprioritize transmission of RLC control PDUs over RLC data PDUs andfurther prioritize retransmission of RLC data PDUs over transmission ofnew AMD PDUs. In retransmission, the transmitting side of an AM RLCentity delivers the AMD PDU if the AMD PDU can entirely fit into the TBof the particular transmission opportunity, otherwise segments the AMDPDU to form a new AMD PDU segment which can fit into the TB.

The MAC layer, a lower layer of the RLC layer supports functions ofmapping between logical channels and transport channels, multiplexing,de-multiplexing, logical channel prioritization, transport formatselection, and so on. An MAC entity of the MAC layer, performing the MACfunctions, exchanges RLC PDUs, seen as MAC SDUs, with the RLC layer vialogic channels and MAC PDUs with the physical layer via transportchannels, such as an uplink shared channel (UL-SCH) or a downlink sharedchannel (DL-SCH). An MAC SDU can be an RLC data PDU, an RLC data PDUsegment or an RLC control PDU. More specifically, the MAC entitymultiplexes MAC SDUs from one or different logical channels onto the TBto be delivered to the physical layer on transport channels. Each MACtransmission is allocated with a transmission time interval (TTI).

In the logical channel prioritization of the MAC layer, a logicalchannel prioritization procedure is applied when a new transmission of ahybrid automatic repeat request (HARQ) process is performed. Eachlogical channel is given a Prioritized Bit Rate (PBR). The PBR is a ratelike X bytes/s or Y bits/s. The logical channel prioritization procedureensures that all the logical channels are served in a decreasingpriority order up to their configured PBR, and if any resources remain,all the logical channels are served in a strict decreasing priorityorder until either the data for that logical channel or the UL grant isexhausted, whichever comes first.

A MAC PDU consists of a MAC header, zero or more MAC SDUs, zero or moreMAC control elements, and optionally padding. Both the MAC header andthe MAC SDUs are of variable sizes. The MAC PDU header consists of oneor more MAC PDU sub-headers, each corresponding to either a MAC SDU, aMAC Control element or padding. MAC PDU sub-headers have the same orderas the corresponding MAC SDUs, MAC Control elements and padding. The MACcontrol elements are always placed before any MAC SDU and padding. Amaximum of one MAC PDU can be transmitted per TB per UE, and one or twoTBs can be transmitted per TTI per UE.

According to the prior art, the MAC selects a TB size for an AM RLCentity, and the TB, onto which the MAC SDUs are multiplexed from one ordifferent logical channels, has the same size as the MAC PDU does. Inthis situation, a problem of TB allocation for RLC entities is incurredin a scenario where more than one RLC entity have data to transmit andlogical channels of these RLC entities are multiplexed in the DL-SCH orUL-SCH. For example, two RLC entities of a UE with equal logical channelpriority have data to transmit and two logical channels of these RLCentities are multiplexed in UL-SCH. The MAC layer has to provide halfthe TB size for each of the RLC entities when both of the RLC entitieshave data, more than half the TB size, to transmission. Therefore, it isunreliable for the RLC SDUs to be segmented and/or concatenated only inaccordance to the TB size selected by MAC. Also, it is unreliable forthe AMD PDU for retransmission to be determined whether to be segmentedonly depended on whether the AMD PDU can entirely fit into thecorresponding TB or not.

The prior art does not clearly specify how to decide the RLC data PDUsize when the RLC control PDU transmission is transmitted in the sametransmission opportunity. Furthermore, the current logical channelprioritization is not clearly defined in the prior art.

SUMMARY OF THE INVENTION

The present invention therefore provides a method and related apparatusof performing transmission and prioritization for packets of an RLClayer for a MAC layer of a wireless communications system.

The present invention discloses a method used in a MAC layer of awireless communications system for performing transmission andprioritization for packets of an RLC layer comprising a plurality of RLCentities coupled to a plurality of logic channels, where the pluralityof logic channel is used for transferring packets between the RLC layerand the MAC layer. The method includes determining a size of a MAC PDUincluding a MAC PDU header and at least a MAC SDU according to a grantprovided by a communications layer lower than the MAC layer, selectingMAC control elements for use in the MAC PDU header, determining MACsub-headers for use in the MAC PDU header according to the selected MACcontrol elements, determining a total transmission payload sizeaccording to a total size of the control elements and a total size ofthe MAC sub-headers, and allocating a transmission payload size for eachof the plurality of RLC entities according to the total transmissionpayload size, a data volume provided by each of the plurality of RLCentities for transmission, and channel priority of the plurality oflogic channels.

The present invention further discloses a method used in a MAC layer ofa wireless communications system for performing transmission andprioritization for packets of an RLC layer. The method includesdetermining a size of a MAC SDU corresponding to an RLC control PDU,determining a size of a MAC SDU corresponding to an RLC data PDU,determining a size of a MAC SDU corresponding to an RLC data PDUsegment, and prioritizing transmission of the RLC control PDU with thefirst priority, transmission of the RLC data PDU and the RLC data PDUsegment for retransmission with the second priority, and transmission ofthe RLC PDU for a new transmission with the third priority.

These and other objectives of the present invention will no doubt becomeobvious to those of ordinary skill in the art after reading thefollowing detailed description of the preferred embodiment that isillustrated in the various figures and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a flowchart of a process according to an embodimentof the present invention.

FIG. 2 illustrates a flowchart of a payload size determining processused in the process of FIG. 1 according to an embodiment of the presentinvention.

FIG. 3 illustrates a flowchart of a payload size determining processused in the process of FIG. 1 according to another embodiment of thepresent invention.

FIG. 4 illustrates a flowchart of a process according to an embodimentof the present invention.

DETAILED DESCRIPTION

Please refer to FIG. 1, which illustrates a flowchart of a process 10according to an embodiment of the present invention. The process 10 isapplied to a MAC layer of a communications system, such as long-termevolution (LTE) wireless communications system, and used for performingtransmission and prioritization for RLC packets of an RLC layerincluding a plurality of RLC entities coupled to a plurality of logicchannel transferring packets between the RLC layer and the MAC layer.The RLC entity preferably operates in AM or UM and the RLC packets canbe RLC control PDUs, RLC data PDUs and RLC data PDU segments. Theprocess 10 includes the following steps:

Step 100: Start.

Step 102: Determine a size of a MAC PDU including a MAC PDU header andat least a MAC SDU according to a physical layer grant provided by aphysical layer.

Step 104: Select MAC control elements for use in the MAC PDU header.

Step 106: Determine MAC sub-headers for use in the MAC PDU headeraccording to the selected MAC control elements.

Step 108: Determine a total transmission payload size (TTPS) accordingto a total size of the control elements and a total size of the MACsub-headers.

Step 110: Allocate a transmission payload size (TPS) for each of theplurality of RLC entities according to the TTPS, a data volume providedby each of the plurality of RLC entities for transmission, and channelpriority of the plurality of logic channels.

Step 112: End.

According to the process 10, the MAC PDU size, as well as a TB size, isdetermined according to the physical layer grant including bandwidth,modulation, coding scheme, and so on, in the next transmission timing.Each MAC SDU in the MAC PDU is preferably an RLC control PDU, an RLCdata PDU or an RLC data PDU segment. The control elements included inthe MAC PDU header and related MAC sub-headers are selected in the nexttransmission timing as well. The TTPS is determined for the plurality ofAM or UM RLC entities according to the total size of the controlelements and the total size of the MAC sub-headers. Preferably, the TTPSis determined to be (the MAC PDU size−the total size of the controlelements−the total size of the MAC sub-headers). One TPS is allocatedfor each RLC entity according to the TTPS, the RLC data volume providedby each of the plurality of RLC entities for transmission, and thechannel priority of the plurality of logic channels. In other words, thewhole size of the MAC SDUs in the MAC PDU is the sum of the TPSsallocated to all the RLC entities.

Preferably, the TPS consist of a first payload size TPS1 for the firstround TPS allocation and a second payload size TPS2 for the second roundTPS allocation. When the sum of all the first payload sizescorresponding to the plurality of RLC entities fits the TTPS after allthe plurality of RLC entities have been served for packet transmissionin the first round, the second round of the TPS allocation will not beperformed, and thereby the second payload size for each of the pluralityof RLC entities is determined to be zero.

In addition, the TPS allocation for the plurality of RLC entities isperformed from the highest channel priority level to the lowest channelpriority level. Each logic channel is given a prioritized bit rate (PBR)whose value varies depended on the corresponding logic channel prioritylevel.

Please refer to FIG. 2, which illustrates a flowchart of a process 20used in the process 10 according to an embodiment of the presentinvention. The process 20 is applied to an RLC entity REi correspondingto a logical channel priority i and a prioritized bit rate PBRi forderiving the first payload size TPS1 i, where i is 1 to the number ofthe RLC entities. The process 20 includes the following steps:

Step 200: Start.

Step 202: Determine a PBR ratio=(PBRi)/(Sum of the PBRs of all RLCentities).

Step 204: Determine a permitted data volume by selecting a value between{a remaining TTPS×a PBR ratio−d1, the remaining TTPS×the PBR ratio+d2}.

Step 206: TPS1 i=min {a data volume of the RLC entity REi, the permitteddata volume}.

Step 208: The remaining TTPS=the remaining TTPS−TPS1 i.

Step 210: The remaining data volume of the RLC entity REi=the datavolume of the RLC entity REi−TPS1 i.

Step 212: End.

In the abovementioned steps, d1 and d2 are tolerance volumes, preferablyratios of (the remaining TTPS×the PBR ratio), such as 5% of (theremaining TTPS×the PBR ratio). The tolerances d1 and d2 can be equal.For example, if the RLC entity REi has 65 byte data to transmit and theresult of (the remaining TTPS×the PBR ratio) is 64 bytes, the d2 can beadjusted to be larger than 1. Therefore, the possible maximum value ofthe permitted data volume is lifted to 65 bytes, and TPS1 i can beallocated with 65-byte capacity, exactly enough for the data needed tobe transmitted.

TPS1 i is the minimum data volume of the data volume of the RLC entityREi and the permitted data volume determined in Step 204. For the RLCentity REi, the remaining data volume is obtained by deducting the TPS1i from the data volume of the RLC entity REi. Similarly, the remainingTTPS is a remaining payload size obtained by deducting all the TPS1 s,allocated for the RLC entities whose priorities are higher than the RLCentity REi, from the TTPS. The initial value of the remaining TTPS isthe TTPS value. For the first RLC entity to be served, the remainingTTPS is equal to the TTPS.

When the RLC entity REi executes the process 20, the remaining TTPSobtained at Step 208 is reused by next RLC entity for the remaining TTPSof Step 204. For example, the TTPS is 100 bytes with 30-byte TPS1 ₁allocated to the RLC entity RE1 and the data volume of the RLC entityRE1 is 120 bytes. In this situation, when the RLC entity RE1 executesthe process 20, the calculation result of the remaining TTPS, which isleft for the RLC entity RE2 to use in Step 204, is (100−30)=70 bytes.The calculation result of the remaining data volume of the RLC entityRE1 in step 210 is (120−30)=90 bytes. The RLC entity RE2 and the RLCentities with lower priority levels execute the process 20 in the sameway as the RLC entity RE1.

Preferably, the total data volume is a summed volume of the RLC controlPDUs, MAC sub-headers corresponding to the RLC control PDUs, RLC PDUsfor retransmission, MAC sub-headers corresponding to the RLC PDUs forretransmission, RLC PDU segments for retransmission, MAC sub-headerscorresponding to the RLC PDU segments for retransmission, one new RLCPDU, and a MAC sub-header corresponding to the new RLC PDU.Alternatively, the total RLC data volume is a summed volume of the RLCcontrol PDUs, RLC PDUs for retransmission, RLC PDU segments forretransmission, and one new RLC PDU.

For data transfer priority in a logical channel, the RLC control PDU isthe first order to be transferred to the MAC layer and included in theMAC PDU, the RLC PDU or the RLC PDU segment for retransmission is thesecond order, and the new RLC PDU is the third order.

Please refer to FIG. 3, which illustrates a flowchart of a process 30used in the process 10 according to another embodiment of the presentinvention. The process 30 is an alternative to the process 20, andthereby the corresponding symbols of the process 30 are defined in thesame way as those of the process 20. The process 30 includes thefollowing steps:

Step 300: Start.

Step 302: Determine a permitted data volume by selecting a value between{PBRi×TTI−d1, PBRi×TTI+d2}.

Step 304: TPS1 i=min {a data volume of the RLC entity REi, the permitteddata volume}.

Step 306: The remaining TTPS=the remaining TTPS−TPS1 i.

Step 308: The remaining data volume of the RLC entity REi=the datavolume of the RLC entity REi−TPS1 i.

Step 310: End.

Compared to the process 20, no PBR ratio is used in the process 30, andthe determination of the permitted data volume is changed to select thevalue between {PBRi×TTI−d1, PBRi×TTI+d2}. The rest of the process 30works in the same way as the corresponding steps of the process 20 do,and therefore the related detailed explanation is omitted herein.

After all the TPS1 s are determined as well as the first round servingall the RLC entities, the sum of all the first payload sizescorresponding to the plurality of RLC entities may be equal to orsmaller than the TTPS. When the sum of all the first payload sizes isequal to the TTPS, meaning that the TTPS is fully utilized, the secondpayload size TPS2 for each RLC entity is determined to be zero. As aresult, the TPS for an RLC entity is exactly the first payload sizeTPS1. On the other hand, when the sum of all the first payload sizes issmaller than the TTPS, meaning that there is still remaining space inthe TTPS, the second payload size TPS2 for each RLC entity has to bedetermined as well as the second round serving all the RLC entities, soas to fully utilize the TTPS.

Similar to the determination of the first payload size TPS1, the secondpayload size for each RLC entity is also determined from the highestchannel priority level to the lowest channel priority level. Thedetermination of a second payload size TPS2 i for an RLC entity REicorresponding to a logical channel priority i and a prioritized bit ratePBRi can be achieve by the followings:

TPS2 i=min {the remaining data volume of the RLC entity REi, theremaining TTPS}; and

The remaining TTPS 32 the remaining TTPS−TPS2 i.

In the abovementioned determination, the second payload size TPS2 i usesa minimum data volume of the remaining data volume of the RLC entity REiand the remaining TTPS. In addition, the remaining TTPS used for thefirst-served RLC entity in the second round is the final volume left bythe end of the first round using the process 20 or 30.

Please refer to FIG. 4, which illustrates a flowchart of a process 40according to an embodiment of the present invention. The process 40 isapplied to the MAC layer of a communication system, such as LTE wirelesscommunications system, for performing transmission and prioritizationfor RLC packets and includes the following steps:

Step 400: Start.

Step 402: Determine a size of a MAC SDU corresponding to an RLC controlPDU.

Step 404: Determine a size of a MAC SDU corresponding to an RLC dataPDU.

Step 406: Determine a size of a MAC SDU corresponding to an RLC data PDUsegment.

Step 408: Prioritize transmission of the RLC control PDU with the firstpriority, retransmission of the RLC data PDU and the RLC data PDUsegment with the second priority, and transmission of a new RLC PDU withthe third priority.

Step 410: End.

According to the process 40, the MAC SDU sizes corresponding to the RLCcontrol PDU, the RLC data PDU or the RLC data PDU segment are alldetermined in the MAC layer. Besides, the transmission of the RLCcontrol PDU, the retransmission of the RLC data PDU and the RLC data PDUsegment and the transmission of the new RLC PDU are prioritized with thefirst, second, and third priority, respectively. Therefore, the RLCentity has to transmit data (ex. the RLC data PDUs or RLC control PDUs)according to the MAC SDU size determined through the process 40. Inaddition, the logic channel priority for transmission of the RLC dataPDUs and RLC control PDUs is clearly determined in the MAC layer.

The method (ex. The process 10 including the process 20 or 30 or theprocess 40) of the present embodiment can also be embodied as computerprogram product on a computer readable recording medium. The computerreadable recording medium is any data storage device that can store datawhich can be thereafter read by a processor of a computer system, suchas the above-mentioned UE, UTRAN or Node-B. Examples of the computerreadable recording medium include read-only memory (ROM), random-accessmemory (RAM), CD-ROMs, magnetic tapes, floppy disks, optical datastorage devices, and carrier waves (such as data transmission throughthe Internet).

In conclusion, the embodiments of the present invention provides methodsaiming to determine MAC SDU sizes for the RLC control PDU, RLC dataPDU/PDU segment in the MAC layer, and furthermore allocate the payloadsizes for the RLC entities according to the determined logic channelpriority when the RLC control PDUs and the RLC data PDU need to betransmitted in the same opportunity.

Those skilled in the art will readily observe that numerousmodifications and alterations of the device and method may be made whileretaining the teachings of the invention.

1. A method used in a medium access control, hereinafter called MAC,layer of a wireless communications system for performing transmissionand prioritization for packets of a radio link control, hereinaftercalled RLC, layer comprising a plurality of RLC entities coupled to aplurality of logic channel, the plurality of logic channel transferringpackets between the RLC layer and the MAC layer, the method comprising:determining a size of a MAC protocol data unit, hereinafter called PDUaccording to a grant provided by a communications layer lower than theMAC layer, the MAC PDU comprising a MAC PDU header and at least a MACservice data unit; selecting MAC control elements for use in the MAC PDUheader; determining MAC sub-headers for use in the MAC PDU headeraccording to the selected MAC control elements; determining a totaltransmission payload size according to a total size of the MAC controlelements and a total size of the MAC sub-headers; and according to thetotal transmission payload size, a data volume provided by each of theplurality of RLC entities for transmission, and channel priority of theplurality of logic channels, allocating a transmission payload size foreach of the plurality of RLC entities.
 2. The method of claim 1,wherein, according to the total transmission payload size, the datavolume provided by each of the plurality of RLC entities fortransmission, and the channel priority of the plurality of logicchannels, allocating the transmission payload size for each of theplurality of RLC entities comprises: allocating the transmission payloadsize comprising a first payload size and a second payload size for eachof the plurality of RLC entities from the highest channel priority levelto the lowest channel priority level; determining a permitted datavolume for each of the plurality of RLC entities; and when the pluralityof RLC entities are served for packet transmission for the first round,using a minimum data volume of the data volume of each of the pluralityof RLC entities and the corresponding permitted data volume as the firstpayload size corresponding to a corresponding RLC entity.
 3. The methodof claim 2, wherein the permitted data volume is determined to be avalue between a range whose lower bound is a remaining totaltransmission payload size multiplied by a prioritized bit rate ratio andthen subtracting a first tolerance and whose upper bound is theremaining total transmission payload size multiplied by the prioritizedbit rate ratio and then added with a second tolerance, wherein theprioritized bit rate corresponds to the priority of the correspondinglogic channel, and the remaining total transmission payload size is aremaining data volume obtained by deducting all of the allocatedtransmission payload sizes corresponding to the higher priority levelsfrom the total transmission payload size, and the prioritized bit rateratio is obtained by a prioritized bit rate of the corresponding RLCentity dividing a sum of the prioritized bit rates of the plurality ofRLC entities.
 4. The method of claim 2, wherein the permitted datavolume is determined to be a value between a range whose lower bound isa transmission time interval multiplied by a prioritized bit rate andthen subtracting a first tolerance and whose upper bound is thetransmission time interval multiplied by the prioritized bit rate andthen added with a second tolerance, wherein the prioritized bit ratecorresponds to the priority of the corresponding logic channel.
 5. Themethod of claim 2, wherein the second payload size for each of theplurality of RLC entities is zero when the sum of all the first payloadsizes corresponding to the plurality of RLC entities fits the totaltransmission payload size after all the plurality of RLC entities havebeen served for packet transmission in the first round.
 6. The method ofclaim 2 further comprising determining the second payload size for eachof the plurality of RLC entities when the sum of all the first payloadsizes corresponding to the plurality of RLC entities is smaller than thetotal transmission payload size after all the plurality of RLC entitieshave been served for packet transmission in the first round.
 7. Themethod of claim 6, wherein determining the second payload size for eachof the plurality of RLC entities comprises: determining the secondpayload size for each of the plurality of RLC entities from the highestchannel priority level to the lowest channel priority level; and using aminimum data volume of the remaining data volume of each of theplurality of RLC entities and a remaining total transmission payloadsize as the second payload size corresponding to a corresponding RLCentity; wherein the remaining data volume of each of the plurality ofRLC entities is obtained by deducting the corresponding first payloadsize from the data volume of each of the plurality of RLC entities. 8.The method of claim 1, wherein the packets of the RLC layer comprises atleast one of RLC control PDUs, RLC data PDUs and RLC data PDU segments.9. The method of claim 8, wherein the at least a MAC service data unitis an RLC control PDU, an RLC data PDU or an RLC data PDU segment. 10.The method of claim 8, wherein the RLC control PDUs are the first orderto be transferred to the MAC layer, the RLC data PDUs are the secondpriority to be transferred to the MAC layer and the RLC data PDUsegments are the third priority to be transferred to the MAC layer. 11.The method of claim 10, wherein the data volume provided by each of theplurality of RLC entities for transmission is a summed volume of the RLCcontrol PDUs, MAC sub-headers corresponding to the RLC control PDUs, RLCdata PDUs for retransmission, MAC sub-headers corresponding to the RLCdata PDUs for retransmission, RLC data PDU segments for retransmission,MAC sub-headers corresponding to the RLC data PDU segments forretransmission, one new RLC data PDU, and a MAC sub-header correspondingto the new RLC data PDU.
 12. The method of claim 10, wherein the datavolume provided by each of the plurality of RLC entities fortransmission is a summed volume of the RLC control PDUs, RLC data PDUsfor retransmission, RLC data PDU segments for retransmission, and onenew RLC data PDU.
 13. The method of claim 1, wherein determining thetotal transmission payload size according to the total size of thecontrol elements and the total size of the MAC sub-headers comprisesdetermining the total transmission payload size to be a payload sizeobtained by subtracting both of the total size of the control elementsand the total size of the MAC sub-headers from the size of the MAC PDU.14. The method of claim 1, wherein the plurality of RLC entitiesoperates in an acknowledged mode or an unacknowledged mode.
 15. Acomputer program product arranged for causing a processor to execute themethod of claim
 1. 16. A method used in a medium access control,hereinafter called MAC, layer of a wireless communications system forperforming transmission and prioritization for packets of a radio linkcontrol, hereinafter called RLC layer, the method comprising:determining a size of a MAC service data unit, hereinafter called SDU,corresponding to an RLC control protocol data unit, hereinafter calledPDU; determining a size of a MAC SDU corresponding to an RLC data PDU;determining a size of a MAC SDU corresponding to an RLC data PDUsegment; and prioritizing transmission of the RLC control PDU with thefirst priority, retransmission of the RLC data PDU and the RLC data PDUsegment with the second priority, and transmission of a new RLC PDU withthe third priority.
 17. A computer program product arranged for causinga processor to execute the method of claim 16.